Dynamics of mather type plasma focus with step anode configuration

Abstract

The tube parameters are of importance to the dynamical properties of plasma as it undergoes the axial and the final pinch phase in a plasma focus. Neutron yield of the plasma focus is dependent on plasma dynamics. The study was aimed to investigate the plasma dynamical behaviour of deuterium gas in Mather type plasma focus with step anode configuration in order to enhance the neutron yield. The model is based on the Lee code version RADPFV5.15FIB under Visual Basic program. The equation of motion of the current sheath was derived for the step anode configuration based on snowplow model and slug model. In this numerical study, the modified Lee model was used to describe the dynamics of current sheath between the outer electrodes and inner electrode with step configuration based on momentum conservation of swept gas. The plasma inductance development from numerical analysis was found to be consistent with the plasma sheath motion across the coaxial tube which gives the total static inductance equal to 104.5 nH and the stray resistance equal to 8.5 mΩ. Numerical experiments has been carried out between the step anode configuration plasma focus system and the cylindrical anode configuration plasma focus system which showed that the step anode configuration system is able to enhance the plasma sheath speed by 42.4 % from the cylindrical anode configuration. The neutron yield from the cylindrical anode configuration system with the effective anode length of 173 mm showed an optimum values of neutron yield of 1.212×108 neutrons from various anode diameters at 3.3 mbar. It was found that due to the speed enhancement, the neutron produced from the step anode configuration system was also increased by 8.2 % at its optimum pressure. In conclusion, the neutron yield is significantly enhanced in step anode configuration of the Mather type plasma focus.